1) Technical Field
The subject invention generally relates to a method of utilizing a sensing technology that monitors an integral operating parameter, such as torque observer sensing which monitors motor torque, within a robot assembly in various robot control and calibration applications.
More specifically, these various robot control and calibration applications include, but are not limited to, determining the position of a workpiece or other external object in an operating space of a robot assembly, determining contact positions of the robot assembly relative to the external objects, determining and adjusting a tool frame of the robot assembly, determining calibration parameters for the robot assembly, determining a working, or reference, frame of the robot assembly which assists in determining the position of the workpiece within the operating space, and the calibration of the robot assembly. The subject invention may also incorporate a sensing device in place of the sensing technology for determining the calibration parameters and the reference frame.
2) Description of the Prior Art
Various control and calibration methods for robots as well as the apparatuses used for such methods are known in the art. For instance, the control method and apparatus for determining contact and maintaining contact between a robot and an object is known in the art. As appreciated, such conventional methods and apparatuses are typically critical to the safe and optimal utilization of a robot in applications such as are welding, spot welding, waterjet cutting, and dispensing.
An example of such a conventional method and apparatus is disclosed in U.S. Pat. No. 5,562,843 to Yasumoto. Specifically, the ""843 patent to Yasumoto discloses an external contact sensor for a robot that senses contact with a conductive object. Upon sensing the conductive object, a robot controller, in communication with the contact sensor, immediately ceases operation and movement of the robot in order to prevent the robot from colliding with an unintended object and to ensure a safe operating environment.
A further example of such a conventional method and apparatus is disclosed in U.S. Pat. No. 4,670,641 to Porsander et al. Specifically, the ""641 patent to Porsander et al. discloses a welding robot having a robot arm. A welding gun is disposed on the robot arm, and a sensing wheel arrangement is provided with the welding gun to assist the welding gun in following a contour of a workpiece. As a result, optimal welding of a weld joint is ensured regardless of the contour of the workpiece or even the continuity of the weld joint.
Notice that, in order to determine or maintain contact between the robot and an object, the sensing technologies of the prior art require additional devices that are peripheral to the robot apparatus. More specifically, the ""843 patent to Yasumoto requires the contact sensor and the ""641 patent to Porsander requires the sensing wheel arrangement to sense contact between the robot and the object. With such additional equipment required to determine or maintain contact, there is a greater likelihood that the methods and apparatuses of the prior art will not accurately determine or maintain contact between the robot and the workpiece due to potential failures of and interferences with this additional equipment.
Such conventional methods and apparatuses are further deficient in that they do not xe2x80x98activelyxe2x80x99 utilize a sensing technology that monitors an integral operating parameter, such as torque observer sensing, in the various robot control and calibration technologies. Most importantly, although these conventional methods and apparatuses may apply a sensing technology to determine and maintain contact between the robot and the object, they are deficient in that they do not xe2x80x98activelyxe2x80x99 utilize contact between the robot and an object or a workpiece with a sensing technology to determine a location of the object or workpiece in the operating space of the robot. Further, the conventional methods and apparatuses do not utilize a sensing technology to monitor an integral operating parameter to determine contact positions of the robot relative to the external objects, to determine and adjust a tool frame of the robot, to determine calibration parameters for the robot, to determine a working, or reference, frame of the robot, or to calibrate the robot.
Instead, the conventional methods and apparatuses merely determine or maintain contact between the robot and the workpiece or object. Specifically, the conventional methods and apparatuses do not xe2x80x98activelyxe2x80x99 determine the location and position of the workpiece or object in the operating space of the robot, or they require costly peripheral equipment. For example, the method and apparatus disclosed in the ""843 patent to Yasumoto does not even monitor an integral operating parameter of the robot, such as motor torque. Instead, the apparatus employs an external contact sensor and merely xe2x80x98stopsxe2x80x99 when contact is sensed at the contact sensor. Further, the method and apparatus in the ""843 patent does not determine the location and position of the object or workpiece that the external sensor contacts.
The conventional methods and apparatuses also do not disclose a method for determining calibration parameters, such as a tool frame or tool center point (TCP) of the robot, using a calibration plaque having a bounded void as in the subject invention. In particular, although U.S. Pat. No. 5,910,719 to Thorne provides a calibration plaque in the operating space of the robot, the method disclosed in the ""719 patent to Thorne only utilizes flat surfaces of the calibration plaque. As such, the ""719 patent to Thorne is deficient because it can only determine a location of the TCP, it can not determine the location and orientation of the TCP as with the calibration plaque having bounded voids of the subject invention.
Due to the limited application of conventional methods and apparatuses, as evidenced by the inefficiencies identified above, it is desirable to implement novel methods that do not require additional equipment to sense contact between a robot and an object or workpiece by monitoring integral operating parameters of the robot. It is additionally desirable that such a method xe2x80x98activelyxe2x80x99 utilize contact between the robot and the object or workpiece to determine a location of that object in the operating space of the robot. It is further desirable to introduce methods that determine calibration parameters and reference frames for robot assemblies utilizing contact between the robot and the object or workpiece and a sensing device.
A method of determining a contact position of a robot assembly relative to an object external to the robot assembly is disclosed. The robot assembly includes at least one arm having a contact surface. The robot assembly further includes a robot controller.
The method of the subject invention includes the step of moving the robot assembly from an initial position toward the contact position. More specifically, at the initial position, the contact surface is spaced from the external object, and at the contact position, the contact surface of the robot arm contacts a point on the external object. The method further includes the step of determining operating values of the robot assembly as the robot assembly moves between the initial position and the contact position. Additionally, at least one operating parameter threshold is established. With the operating parameter threshold established, the operating values can be compared to the established threshold. To determine the contact position of the robot assembly according to the subject invention, the movement of the robot assembly is continued so long as the operating values are less than or equal to the operating parameter threshold. The contact position of the robot assembly is recorded when the operating values exceed the operating parameter threshold.
The subject method invention is characterized by monitoring an integral operating parameter to determine the operating values of the robot assembly. That is, the step of determining operating values is further defined as monitoring the integral operating parameter within the robot assembly during the movement of the robot assembly between the initial position and the contact position. Monitoring the integral operating parameter determines when the robot assembly contacts the external object.
Similar methods according to the subject invention may be employed to determine calibration parameters of the robot assembly and to determine a reference frame in an operating space of the robot assembly. More specifically, to determine a calibration parameter, a calibration plaque is mounted within the operating space of the robot assembly. The calibration plaque includes an outer facing and at least one calibration element. The calibration element on the calibration plaque defines a bounded void having an inner surface. In this method of the subject invention, the robot assembly incorporates a sensing device that detects contact between the contact surface of the robot arm and the inner surface of the bounded void.
Similar to the above-described method, this method includes the step of moving the robot assembly from the initial position toward the contact position. However, this embodiment of the subject invention is characterized by moving the robot assembly from the initial position where the contact surface is spaced from the inner surface of the bounded void toward the contact position where the contact surface of the robot arm is at least partially extended into the calibration element and contacts a segment on the inner surface of the bounded void.
Once movement of the robot assembly is initiated, in this method, the sensing device detects when the contact surface of the robot arm contacts the segment on the inner surface of the bounded void. As above, movement of the robot assembly is continued until the contact surface contacts the segment. Then, the contact position of the robot assembly relative to the inner surface of the bounded void is recorded when the sensing device detects contact between the contact surface and the segment.
The method to determine the reference frame in the operating space of the robot assembly includes the steps of determining a plurality of contact points relative to the reference frame, and determining a first vector approximately normal to either the contact surface of the robot arm or a contact surface of the external object, referred to as an object contact surface. The first vector is approximately normal either of these surfaces at one of the plurality of contact points. This method further includes the step of determining a geometrical relationship between the robot assembly and at least one of the contact surface and the object contact surface.
Next, as in the previously described methods, the robot assembly is moved from the initial position toward the contact position. However, this embodiment of the subject invention is characterized by moving the robot assembly from the initial position where a second vector, between the contact surface and the contact point, is approximately normal to at least one of the contact surface and the object contact surface along the first vector toward the contact position where the contact surface of the robot arm contacts the object contact surface.
The movement of the robot assembly continues until the sensing device detects contact between the contact surface of the robot arm and the object contact surface, and the contact position of the robot assembly is recorded when the contact is detected by the sensing device.
Accordingly, the subject invention provides novel methods, such as the method of determining the contact position of the robot assembly relative external objects, that eliminate external sensors and xe2x80x98activelyxe2x80x99 utilize the contact positions of the robot assembly to determine the location of the external object in the operating space of the robot assembly by monitoring integral operating parameters, such as motor torque, within the robot assembly. The subject invention also provides a novel method for determining calibration parameters of the robot assembly by incorporating a sensing device to detect contact and moving the contact surface of the robot assembly within a calibration plaque having bounded voids. The subject invention further provides a novel method of determining reference frames for robot assemblies utilizing the sensing device to detect contact between the contact surface on the robot arm and the contact surface of the external object.